Two seizures suffered by a baby girl did not happen naturally, the murder trial of a nurse has been told.
Lucy Letby, 33, is accused of attempting to murder the premature-born infant in her cot at the Countess of Chester Hospital in Chester.
Child J had two "profound" drops in blood oxygen levels on 27 November, 2015 and two further episodes when her heart rate also plunged and she showed signs of a seizure, Manchester Crown Court was told.
Giving evidence on Tuesday, expert medical witness Dr Dewi Evans told prosecutor Nick Johnson KC he could not identify any natural process that may have caused the seizures.
Evans said: "My opinion was that (Child J's) brain was deprived of oxygen for a sufficient level of time to cause hypoxia i.e. loss of oxygen to the brain, causing fits.
"As far as I know this was the only occasion when she had seizures and the cause of this was the hypoxia, the lack of oxygen to the brain."
Johnson asked the retired consultant paediatrician: "So far as the hypoxic incidents that had caused these seizures were concerned, could you identify any natural process that might have caused that?"
Evans replied: "No, I could not. There was no reason why she should suddenly become hypoxic."
Evans agreed with Ben Myers KC, defending, that he could not rule out infection "for sure".
However, fellow expert witness, consultant paediatrician Dr Sandie Bohin, said she had excluded infection.
She told the court: "(Child J) was a well baby. She was ready to go home. Babies who are ready to go home do not have major desaturations which lead to prolonged resuscitation."
Bohin told Myers she had not been able to identify an "obvious cause" for her collapses.
Tests showed no signs of infection and did not identify a cause for the seizures, the court heard.
Child J had previously undergone bowel surgery a day after her birth but medics have said she was stable in the weeks that followed.
On the morning of 27 November, she was being cared for in nursery room four in readiness for returning home to her parents.
Child J was later moved to room two for closer monitoring ahead of the second pair of collapses.
She eventually was discharged in January 2016 and was described as progressing "very well" at her final outpatient clinic more than a year later.
Letby, originally from Hereford, denies murdering seven babies and attempting to murder 10 others between June 2015 and June 2016.
The trial continues.